1. Field of the Invention
This invention relates to a method of and a device for controlling a fuel injection timing in a diesel engine, and more particularly to improvements in a method of and a device for controlling a fuel injection timing in a diesel engine, suitable for use in an electronically controlled diesel engine for a motor vehicle, wherein the maximum injection timing most suitable for the time when the fuel injection reaches the maximum quantity is determined as commensurate to at least an engine speed and an intake air pressure and an injection timing is controlled in accordance with the maximum injection timing.
2. Description of the Prior Art
In general, in a diesel engine, the fuel fed to combustion chamber thereof is controlled by a fuel injection pump rotatably driven in synchronism with the rotation of the engine, and a timer is moved by supply pressure of a feed pump provided in the fuel injection pump so as to move a roller ring, whereby the fuel injection timing is controlled. Furthermore, a spill ring is moved by a centrifugal governor to change the ending time of pressure feed, whereby the fuel injection quantity is controlled. However, since the timer and the spill ring have heretofore been mechanically controlled, it has been difficult to precisely conduct the fuel injection control.
On the other hand, along with the development in the techniques of electronic control, particularly, in the techniques of digital control, the attempt at electronically controlling the fuel injection pump as disclosed in Japanese Patent Laid-Open No. 146023/1981 for example is made. The electronic control of the type described makes it possible to inject the optimal quantity of fuel at the optimal injection timing in accordance with the engine operating conditions such as an engine speed, an engine load and the like.
However, heretofore, in calculating the optimal injection timing commensurate to the intake air pressure, firstly, the basic maximum injection quantity Qfullo has been determined in accordance with the engine speed, the maximum injection quantity Qfull has been calculated by multiplying the basic maximum injection quantity Qfullo by a factor commensurate to the intake air pressure, and the maximum injection timing Tfull then capable of controlling the smoke and preventing the increase in the chamber temperature and exhaust-gas temperature has been determined from the maximum injection quantity Qfull and the engine speed NE, whereby, in order to determine the maximum injection timing Tfull, firstly, it has been necessary to determine the maximum injection quantity Qfull, thus presenting the disadvantage of increasing the steps in the precess of determining the maximum injection timing Tfull.
On the other hand, as an invention similar to the present invention, in Japanese Patent Laid-Open No. 150035/1983, the applicant has proposed a method, wherein a basic injection timing is calculated on the basis of an engine speed, a fuel injection quantity and the like and the basic injection timing is corrected as commensurate to a variation in intake air pressure from a reference intake air pressure. However, this method is not a method of determining the maximum injection timing and has as its object the altitude compensation of the basic injection timing. So, the method has been different in object from the present invention, and moreover, has required to determine the fuel injection quantity in calculating the basic injection timing.